1.. Sequences/Intrinsic Metafunctions//size 2 3size 4==== 5 6Synopsis 7-------- 8 9.. parsed-literal:: 10 11 template< 12 typename Sequence 13 > 14 struct size 15 { 16 typedef |unspecified| type; 17 }; 18 19 20 21Description 22----------- 23 24``size`` returns the number of elements in the sequence, that is, the number of elements 25in the range [``begin<Sequence>::type``, ``end<Sequence>::type``). 26 27 28Header 29------ 30 31.. parsed-literal:: 32 33 #include <boost/mpl/size.hpp> 34 35 36 37Model of 38-------- 39 40|Tag Dispatched Metafunction| 41 42 43Parameters 44---------- 45 46+---------------+-----------------------+-----------------------------------------------+ 47| Parameter | Requirement | Description | 48+===============+=======================+===============================================+ 49| ``Sequence`` | |Forward Sequence| | A sequence to query. | 50+---------------+-----------------------+-----------------------------------------------+ 51 52 53Expression semantics 54-------------------- 55 56 57For any |Forward Sequence| ``s``: 58 59 60.. parsed-literal:: 61 62 typedef size<s>::type n; 63 64:Return type: 65 |Integral Constant|. 66 67:Semantics: 68 Equivalent to 69 70 .. parsed-literal:: 71 72 typedef distance< begin<s>::type,end<s>::type >::type n; 73 74 75:Postcondition: 76 ``n::value >= 0``. 77 78 79 80Complexity 81---------- 82 83The complexity of the ``size`` metafunction directly depends on the implementation of 84the particular sequence it is applied to. In the worst case, ``size`` guarantees a 85linear complexity. 86 87If the ``s`` is a |Random Access Sequence|, ``size<s>::type`` is an |O(1)| operation. 88The opposite is not necessarily true |--| for example, a sequence class that models 89|Forward Sequence| might still give us an |O(1)| ``size`` implementation. 90 91 92Example 93------- 94 95.. parsed-literal:: 96 97 typedef list0<> empty_list; 98 typedef vector_c<int,0,1,2,3,4,5> numbers; 99 typedef range_c<int,0,100> more_numbers; 100 101 BOOST_MPL_ASSERT_RELATION( size<list>::value, ==, 0 ); 102 BOOST_MPL_ASSERT_RELATION( size<numbers>::value, ==, 5 ); 103 BOOST_MPL_ASSERT_RELATION( size<more_numbers>::value, ==, 100 ); 104 105 106See also 107-------- 108 109|Forward Sequence|, |Random Access Sequence|, |empty|, |begin|, |end|, |distance| 110 111 112.. copyright:: Copyright � 2001-2009 Aleksey Gurtovoy and David Abrahams 113 Distributed under the Boost Software License, Version 1.0. (See accompanying 114 file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt) 115